and STRONG-FIELD GRAVITY

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BLACK HOLES
and STRONG-FIELD GRAVITY
DIMITRIOS PSALTIS
University of Arizona
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can BLACK HOLES tell us anything
about STRONG-FIELD GRAVITY?
DIMITRIOS PSALTIS
University of Arizona
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What measures the strength of the gravitational
field?
e.g., in the Schwarzschild spacetime
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What measures the strength of the gravitational
field?
In the opposite extreme, what if we add, e.g., a
cosmological constant?
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Where does Einsteins equation come from?
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How can we extend Einsteins equation?
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TESTS OF GENERAL RELATIVITY
Psaltis 2006
GP-B
Eclipse Hulse-Taylor
Moon
Mercury
Potential (GM/rc2)
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TESTS OF GENERAL RELATIVITY
Psaltis 2006
GP-B
Eclipse Hulse-Taylor
Moon
Mercury
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Scalar-Tensor black holes are identical to GR
ones!
Thorne Dykla 1971 Hawking 1974 Bekenstein
1974 Sheel et al. 1995
all R2 terms
any function of R
in the Palatini formalism
Always get Kerr Black Holes!!!
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We can rely on phenomenological spacetimes
e.g., measure coefficients of multipole
expansions of the metric
Ryan 1995 Collins Hughes 2004
or even measure directly the metric elements from
observations
Psaltis 2007
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Black holes can be used as null-hypothesis tests
against alternative gravity theories that predict
massive compact stars
b
e.g., in scalar-tensor gravity, neutron stars can
be heavy!
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The Good News
We have a parameter-free solution to an
astrophysical problem!
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Large Extra Dimensions?
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XTE J1118480
Mirabel et al. 2001
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Constraining AdS Curvature of Extra Dimensions
Psaltis 2007, PRL, in press
XTE J1118480
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CONCLUSIONS

• (I) Gravity in the Strong-Field Regime has not
  been tested
• (II) Gravitational Fields of Neutron Stars and
  Stellar-Mass
• Black-Holes are the Strongest Found in the
  Universe
• ? a great laboratory to perform
  gravitational tests
• (III) To Learn about Strong-Field Gravity with
  Black Holes
• we have to
• ? Resolve the relevant (msec) dynamical
  timescales
• ? Develop a theoretical framework to
  quantify our results